I. Field of the Invention
The present invention relates generally to methods for determining the absolute angular position of a sensor which produces a repeating periodic analog sensor across a predetermined rotation range.
II. Description of Related Art
There are many different types of applications in industry where it is necessary to determine the absolute angular position of a rotatable actuator across a predetermined rotation range, e.g. 360 degrees. For example, in the automotive industry it is necessary to determine the position of a gearshift actuator and to accomplish automatic recovery of the position of the gearshift actuator upon energization or a power reset of the system. For example, such gearshift actuators are used for many vehicles to shift between two wheel and four wheel drive for the automotive vehicle.
There have been a number of previously known angular position sensors which produce an output signal representative of the angular position of the actuator. For example, in one type of angular sensor, a wiper is secured to and rotates in unison with the actuator. This wiper, in turn, slides across a resistive member so that the resistance between the wiper and one end of the resistive member varies as a function of the rotational position of the wiper and thus the rotational position of the actuator.
One disadvantage of this type of previously known position sensor, however, is that, due to the mechanical contact between the wiper and the resistive member, the sensor suffers mechanical wear, especially after protracted use. Such mechanical wear in the sensor can result in inaccurate and erratic readings from the sensor and even complete sensor failure.
In order to eliminate the mechanical wear of these previously known angular sensors, there have been previously known noncontact sensors. In one type of noncontact sensor, a permanent magnet is mounted to the rotatable actuator so that the permanent magnet rotates in unison with the actuator.
A sensor having a plurality of magnetic resistors is then mounted in alignment but not in contact with the permanent magnet attached to the actuator. These magnetic resistors are arranged in two bridges such that the magnetic resistors provide two sinusoidal output signals offset from each other by 45 degrees and which vary as a function of the angular position of the actuator.
A disadvantage of these previously known sensors utilizing magnetic resistors, however, is that they produce a repeating periodic signal for every 180 degree rotation of the actuator. Consequently, it has not been possible to utilize these previously known sensors with magnetic resistors where the rotation range of the actuator exceeds 180 degrees. This, in turn, necessitated the use of two or more sensors which is prohibitively expensive for many applications.
A still further disadvantage of these noncontact sensors which utilize magnetic resistors is that the sinusoidal output provided by the sensors was not true sinusoidal signals but, rather, approximations of sinusoidal signals. Consequently, even within the 180 degree angular range of the sensor, it was only possible to determine the position of the actuator with an accuracy of plus or minus a few degrees. In many applications, however, it is necessary to determine the absolute angular position of the actuator with greater accuracy, i.e. the absolute angle of the activation even though the absolute angle range of the actuator exceeds the periodic range of the sensor.